I finally made some time to work on a pump. I had an UMS pump that I wanted to convert to a belt drive. I have some other gears to try making my own pumps if this works out.

Here is what it looked like after I disassembled the UMS gear pump from the stock motor.

First I faced the back and then made a bronze stepped bushing. I then made a shaft from 1/4 inch stainless rod. I turned it down to 2.31mm to press fit into the 2.27mm hole (.0015 inch difference) of the gear. You can see a similar shaft and bushing in the photo but those are ones that didn’t work out. I also made an outside collar for the pump housing to give more room for bolt holes, press fit and three 3mm bolts to hold it secure.

Here is the bracket (made from 1x2 block - gotta love how much material a roughing endmill will remove) to hold the motor and gear pump.

Here is the gear pump assembled and bolted to the bracket.

Here is the pump shaft pulley (42t) - bearings on both ends.

And finally with the 800 KV motor (35-48) and drive shaft pulley (14t, I also have a 16t for use with a larger 42-50 size motor) installed. Both shafts are dimpled for the set screws.

All of the pieces

And my DRO (showing the bolt circle pattern program) that made it possible (well, that and my lathe and mill).

I don't remember for sure but I think i got them from McMaster. The belts are 70t MXL 1/4 wide. I have bunch of smaller pulleys in 1/8 and 1/4 size and different lengths of belts but this seemed to be a good starting point. One issue is the size of the motor shaft, the larger 42-50 motors have a 3/16 shaft so the 1/8 bore in the 14t is too small, you need to go up to a 16t to get a 3/16 bore. THe 35-48 motor had a 4mm bore so it was easy to bore out the 14t shaft on my lathe. Fortunately, the larger 42t pulley has a 1/4 bore so it just fits a 1/4 stainless rod.

If I recall, the smaller pulleys are about $9 each and the larger ones are about $12. The belts are only a couple of dollars.

I have a bunch of gears from SDP or maybe it was QTC gears (same owners I think) to try out to make my own gear pump. Maybe sometime over the holidays I will get a chance to build my own gear pump. I already made a second bracket (it doesn't take long with a roughing endmill).

Thanks Richard, I was looking at Mcmaster's website a couple nights back and I saw the pulleys and belts there. How do you find them to order from? I wanted to order the nuts and bolts for my tracks from them but I wasn't sure if the shipping/customs would be too expensive.

We used a gerotor style set of gears to make a mock up pump for my Volvo but so far I've only driven it with a 2600rpm drill so I'm not sure if it will be too hard to turn for an RC size motor. It pumps around 1.2l with no load but only just over half at 25 bar through the relief valve so I'm not sure if that's OK or not? If it doesn't work out we will switch to an external gear pump like you are building.

Fantastic work Richard. looks like the new machines are working out well. I like the setup that you have and I think that will be a lot better that the direct drive. Will be real interested to see the results when you have it running.
Rob

I ended up stripping the inside of the drive gear so never got this going. I am not sure what the problem was but I think the original hole was slightly off center so it didnt quite line up with my lathe centered hole on the bronze bushing. I have been experimenting with some other gears I have but so far haven't had success (for other reasons). Defintely easier just to buy a pump but I am not quite ready to give up yet.